Method of geoboring



Jan. 21, 1969 e. D. CAMP 3,422,912

METHOD OF GEOBORING Filed March 20, 1967 V 4 a i A E? N CONTROL BOX INVENTOR. George D. Com p ATTORNEYS 3,422,912 METHOD OF GEOBORING George D. Camp, Apartado Postal 1005, Mexico City 1, Mexico Continuation-impart of application Ser. No. 413,349, Nov. 23, 1964. This application Mar. 20, 1967, Ser. No. 624,227 US. Cl. 1'75-40 12 Claims int. Cl. E21b 3/00, 21/04; E21c 13/02 ABSACT OF THE DISCLOSURE A method of geoboring by trepanation, geoboring being the boring of earth formations and geological structures of any and all kinds, the method Comprising cutting, as contrasted to crushing or flaking, of a narrow, circular annulus in the earth orgeological structures by means of a trepan carried on the lower end of a'drill stem passing downwardly through a casing, the annulus being only of sufficient width as to afford the minimum necessary flow space for fluid between the casing and the drill stem and between the drill stem and the core cut by the trepan.

Cross-reference to related application This application is a continuation-in-part of my copending application Ser. No. 413,349 filed Nov. 23, 1964, now abandoned, and reference is made thereto.

BACKGROUND OF THE INVENTION Field of the invention The field of the invention is the boring of geological structures by trepanation to very great depths with minimal cutting of the structures and maximal recovery of cores.

Description of the prior art Conventional rotary drilling functions through a crushing and flaking action which disintegrates substantially all of the contents of the borehole. As the depth increases, rotary drilling becomes increasingly costly and time consuming and seems to have a practical depth limit of 8 km. in most formations found at such depths.

Summary j the invention The invention is a new method, process or system for earth boring which is a distinct improvement over present rotary-drilling practices enabling drilling to far greater depths and at less cost. It consists of a combination of a number of basic steps, ,some of which are old, which form the basic method, and several ancillary steps which may be used as convenient to carry out the basic steps to improve the performance and applicability of the basic method. The principal features which distinguish my method from present and past practices are: (1) attaching a suitable wellhead to the top of the casing whereby a drilling fluid may be circulated under controlled pressures both inside and outside the drill string; (2) boring by trepanation with a cutting action, rather than a crushing or flaking action; (3) the removal *by cutting of only a minimal portion of the volume of the borehole and leaving the major portion of the volume to be removed as core; (4) using a drill stem of substantially the same diameters as the trepan; (5 the drilling fluid being under pressure, the usual drilling mud is not necessary and any suitable drilling fluid may be used as required by the various conditions found in the borehole; (6) maintaining the drilling fluid in the borehole and the wellhead continuously under pressure; (7) removing substantially intact cores from the borehole by manipulating the pressures of the drilling fluid to force the cores out of the borehole by piston action; (8) substantially continuous n. 3,612,032 Patented Jan. 21, was

core recovery of substantially complete cores; (9) the severing by lateral hydraulic pressure of standing cores by manipulating the pressures of the drilling fluid; (10) when standing core will not readily break due to pressure alone, manipulating the pressure inside the drill stem so that the friction of the returning drilling fluid and cuttings through the annular space between the drill stem and the standing core creates suflicient pull on the upper portion of standing core to sever it through tension from the lower portion; (11) detecting a sudden change in the differential pressure of the drilling fluid inside and outside the drill stem, which indicates the severance of the standing core, for the purpose of determining the depth at which severance took place and actuating a means for receiving the severed core at the top of the borehole; (12) using nesting sizes of drill strings and cementing each in the borehole when the trepan becomes unserviceable, before inserting the next smaller size for continuation of boring.

Brief description of the drawing FIG. 1 is a schematic view showing an apparatus for carrying out the method of this invention,

FIG. 2 is a longitudinal sectional view of a typical joint of the drill stem, and

FIG. 3 is a longitudinal sectional view of the trepan.

Objects of the invention The prime purpose of this invention is to provide an entirely new system of drilling to reduce the mounting costs of drilling wells and to lighten the equipment used to facilitate moving and setting up, and drilling to depths greater than is economically feasible by present practices.

A further purpose is to permit drilling to depths greater than 8 km. which experience has demonstrated is the limit of economic drilling with the present system. A new system is needed, and this invention is intended to be the answer to that need.

The method of geoboring by trepanation, geoboring being the boring of earth formations and geological structures of any and all kinds, known for over 2,000 years, can be used to substantially reduce the work done in boring as only a smallportion of the material in the borehole is disintegrated, the major part remaining in the hole as a core to be lifted substantially intact by hydraulic or pneumatic means, permitting a great reduction in weight and cost of the drill string, the rig and the drill vessel or platform, thus reducing the cost and time of boring and permitting far deeper boreholes than at present practicable.

Substantially complete core recovery would give geologists invaluable new and complete geological information and would enable more effective use of geophysical prospecting methods, all of which may conceivably reduce materially the cost and time of locating and blocking out mineral, petroleum and sulphur deposits, and may even permit locating deposits not now discoverable. The method not only permits, but makes advisable, larger diameter boreholes than are now economical, thus permitting more complete geological information and straighter holes.

Trepanation also facilitates directional control, as it depends upon cutting rather than crushing, and the drill stem is materially stiffer, being of substantially the same diameter as the trepan.

With modern metals and metallurgy, the trepan cutting edge can be made to last far longer than the present rotary and percussion bits, thus reducing or eliminating the need for pulling the drill string to change bits.

The life of the trepan may be materially increased by interlocking the drill feed with a torque meter and control to limit the load on the trepan to safe limits while keeping it high enough for optimum performance in the geological structure at the drilling horizon, and automatically varying the feed with changes in structure.

With automatic load control and a stiff drill stem, the vibration of the drill stem will be reduced to a minimum and can be controlled by varying the speed of rotation and rate of feed. Also, the amplitude of vibrations is limited by the very small clearance between the trepan and the wall of the borehole.

The use of nesting sizes of trepans and stems provides for very deep boreholes by using successively smaller sizes as each larger sized trepan is consumed and the stem left in the borehole to serve as a casing for the next smaller size, thus avoiding any pulling of drill strings, and reducing the needed capacity of the platform or vessel to that required for the rig and the supply of stem in current use, rather than the complete drill string as would be the case if the whole drill string had to be pulled.

The method readily lends itself to manual, simi-automatic or fully automatic control throughout, specifically to the recovery of cores.

Drilling mud may or may not be used as the pressure in the borehole is retained with any suitable drilling fluid, which may be either one inserted or a natural product of the borehole, this same fluid serving as a cutting fluid as well as a vehicle to carry off the cuttings, and as a fluid to sever and lift the core. It would also serve as operating fluid when the trepan is turbine-driven, which would materially reduce vibration in the drill stern and the power required to overcome inertia in starting.

Drilling mud is a water suspension of bentonite which may contain barite or other minerals for increasing the weight and other minerals or chemicals for other specific functions. It is one of the many drilling fluids in current use, including water and molten sulphur, whose primary function is that of a vehicle for drilling-cuttings. But in the casing it also serves to resist external pressure on the casing due to formation gas and liquids, and also to resist blowouts from high formation pressure, hence the need to increase weight as pressure increases. Mud is a troublesome and costly feature of current drilling practice, partly because of the need to change its characteristics frequently in deep drilling to meet new conditions due to variations in the formation as to pressure, temperature, chemical and physical nature of the formation contents, etc. One great advantage of my method is that mud is not necessary, for it functions with drilling fluid (any suitable drilling fluid) under pressure both inside and outside of the drill stern and hence does not need mud to hold down formation pressures, and any other drilling fluid which can serve as a lubricant and vehicle for cuttings may be used. In the absence of any other suitable drilling fluid, mud could be used but it would be a superfluous luxury and defeat some of the advantages of my method.

No slush pit, mud line, nor mud ditch is needed, nor is the usual store of mud components needed, which will reduce the cost and weight of the supplies and drilling rig, as well as other equipment. In short, this method opens new fields of activity of incalculable value which are inaccessible with present methods.

Description of the preferred embodiments As this invention is of a new system of drilling which is an improvement on the present system, in the following description and in the claims those steps which are familiar to those persons versed in the art of the present system are not described in detail and should be construed as those common to present practices.

This invention relates to the method of geoboring with trepanation and substantially continuous core recovery. It relates only indirectly to the machinery and equipment for carrying out the method, which are covered by divers subordinate inventions. The method is described as follows:

As in current rotary drilling practice, a casing 1 (conductor pipe) of suitable size and diameter is sunk in the usual manner through the loose surface material to a firm geological formation and so cemented in place as to resist the upward pressure of the drilling fluid and/or natural materials under pressure which may be encountered in boring, and so cemented in place as to avoid loss of pressure outside of the casing from the lower end thereof. The casing should be of such wall thickness and material as to safely withstand the pressures developed during boring.

To the upper end of the casing 1 (FIG. 1) is firmly fixed a wellhead 2 of suitable design -with an opening so arranged as to admit a trepan 3 (FIG. 3) and drill stem 4 and at the same time retain the drilling fluid and borehole products, the wellhead having an opening as at 5 to admit the drilling fluid and another for gaging and control of the drilling fluid pressure, and such other devices, contrivances and appliances as may be desirable to carry out the method.

Through the wellhead 2 is admitted to the casing 1 the cylindrical trepan 3 comprising a cutting edge 6 (FIG. 3) and a body within an outside diameter only sufficiently less than the inside diameter of the casing to allow the passage through the annular space between the casing and the trepan body of the required amount of drilling fluid. The trepan is provided with teeth 7 of suitable design and arrangement to cut an annular groove in the geological formation to be bored and leaving an annular space between the core and the interior of the trepan only sufficient for the passage of the driiling fluid and cuttings.

The essential difference between my method and previous practice is in the mode of drilling. Trepans and trepanation are very old, but I have found no record of the use of trepans with a cutting action (as in metal working) in rock boring: saw-tooth bits with a scraping action are used in clays and soft rock, or with a rending action as in sand, gravel and conglomerate; trepans with diamond or carbide inserts are regularly used for core drilling, but they usually have no cutting edges and their action is the same as that of the roller rock bits, crushing under the inserts and flaking in the areas surrounding the inserts. All rocks seem to undergo transformation under high pressure and become progressively more plastic with pressure (depth, in situ), making them less fragile which accounts for the increased difficulty of drilling with roller bits below 6 km. depth and is making the practicable limiting depth of present drilling practice something of the order of 8 km., whereas my method of boring by cutting comes into its own at depths where the transformation begins to take place and the more plastic the rock becomes the more readily it is bored by my method.

The extension of the teeth 7 of the trepan 3 (FIG. 3) from the outer surface of the trepan body should be such as to leave an annular space between the wall of the borehole and the trepan body only sufficient to avoid binding in the borehole and allow the passage of the required amount of drilling fluid to lubricate the passage of the stem through the borehole and carry out the cuttings. The extension .of the teeth inward should be such as to leave an annular space between the trepan body and the core only sufficient to permit the upward passage of the drillingfluid and cuttings, and should be so restricted that the friction due to the upward passage of the fluid and cuttings will tend to throttle the upward flow of the drilling fluid and cuttings and require increasing the pressure of the drilling fluid outside the drill stem and trepan in order to maintain sufficient flow of drilling fluid for proper cutting of the trepan, until the pressure itself around the core is sufficient to sever the core, or as in some fisjsured or porous structures to force the drilling fluid into a natural or induced crevice or discontinuity in the standing core and sever it. The differential pressure of the drilling fluid between the zone of severance and the top of the standing core then drives the severed core as a piston to the well-head.

To the butt end of the trepan 3 is connected the drill pipe or stem 4 of uniform inside and outside diameters substantially the same as those of the trepan body. Successive sections of stem are added as necessary for the trepan to reach the bottom of the borehole.

A suitable drilling fluid is inserted through the wellhead 2 (FIG. 1) to fill the borehole, both inside and outsidethe drill stem, the pressure in the drilling fluid outside the .drill stem being maintained slightly higher than the formation pressure in the borehole, while the pressure inside the drill stem is reduced in order to induce the circulation of the drilling fluid from outside to inside the trepan, up through the wellhead to a separator (not a part of this invention) for removing cuttings and core, and returned to the wellhead under pressure.

With the trepan on the bottom, to the stem before the wellhead are attached yokes 8 and other devices 9 (not parts of this invention) to rotate the drill stem and the trepan by means of a suitable prime mover 10 (not a part of this invention), to control its position and movement either mechanically or hydraulically, to recover the core as forced to top of the stem, to control the pressure of the fluid inside the stem for allowing the core to rise and for cont-rolling the flow of the drilling fluid through the cutting edges of the trepan, and to receive the fluid for separation of cuttings and re-use.

The control of advance of the stem may be interlocked with a suitable torque control device 11 (FIG. 1) on the rotational drive 9 to control automatically the torque within the desired limits and admit of optimum drilling speed by increasing or decreasing the pressure urging the trepan against the rock structure being drilled. Torque control devices, such as shown in US. Patents Nos. 1,703,234, 1,935,105 and 2,314,560, are adaptable for use in this method.

The drill string, composed of the trepan, the drill stem, the turbine if used, and such other equipmentand instruments as may be attached thereto, is lifted slightly to free the trepan from the bottom of the borehole, the flow of the drilling fluid started down the outside of the stem and up the inside, rotation of the stem is started and when it reaches normal boring speed the stem is lowered slowly until the trepan cuts smoothly. The pressure of the drilling fluid both outside and inside the drill stem are so adjusted as to provide a suitable flow of the fluid through the trefpan, and then the apparatus may be switched over to the automatic torque and feed control referred to in the previous paragraph.

When boring in weak or fractured structures the pieces of core naturally detached in the normal course of boring are transported with the cuttings by the returning drilling fluid to above ground where they are recovered in a suitable sample-collecting device (not a part of this invention).

As standing c'ore accumulates in relatively sound formations which are not readily subject to incipient fracture and the core remains standing, the pressure of the drilling fluid inside the drill stem at the wellhead will tend to drop relative to that inside the wellhead and outside the drill stem, and will require an increase in the wellhead pressure to maintain the necessary flow of the drilling fluid to carry away the cuttings, this adjustment of pressure being eflected either manually or automatically by devices not forming a part of this invention. This loss of pressure inside the drill stem due to the friction of the returning driliing fluid and cuttings through the narrow annular space between the inside of the drill stern and the standing core may create suflicient upward pull on the standing core to sever it through tension at a plane of weakness, and the severed portion will be driven in the manner of a piston to a core-catcher device (not a part of this invention) above ground. This action takes place while boring continues normally, but it can be brought about intentionally to sever cores of ductile nature.

Should the standing core in sound formation not readily subject to incipient fracture accumulate so, as to threaten difficulty of handling the core above ground, or should it be desired for any other reason to sever the core at will, the pressure of the drilling fluid entering the borehole may be increased until the lateral hydraulic pressure on the body of the core is sufficient to sever it, which severance will usually take place near the base of the standing core where the pressure is greatest for not having been reduced by the friction of the rising drilling fluid and cuttings. Recent research on sever-ing core protected by a thin metallic sheath under hydraulic pressure around the sheath has confirmed that cores can be severed by lateral hydraulic pressure without the fluid coming in contact with the core. Once severed, the pressure of the drilling fluid will force the severed core to above ground by piston.

action, the pressure of the drilling fluid outside the stem dropping suddenly and that inside above the standing core rising, thus determining the moment of severance, and the length of the drill string in the borehole at that moment determines with considerable accuracy the hori- Zon at which severance took place.

In addition to a torque meter, many other suitable metering, recording and controlling devices (the devices themselves not forming a part of this invention) may be used with this method. The use of such devices is very advantageous for controlling the torque on the trepan and on the drill stem created by the boring action of the trepan in order to maintain the optimum pressure of the trepan on the formation and the speed of rotation for maximum economy of boring, with due regard to safety and all other factors. As is well-known, such devices may be used to assist manual operation of the apparatus or to supplant manual operation and may be utilized to pr0- vide fully-automated operation of the whole method, something similar to the operation by the operator of an automated continuous rolling mill in a steel plant where the prime function of the operator is to push a button to stop the mill when the automatic devices are unable to keep it operating normally.

Due to the pressure drop in the drilling fluid because of friction as the fluid passes upwardly through the annulus between the core and the drill stem and due to the decrease in such pressure drop when the core severs, the pressure at the top of the drill stem may be observed or detected and a rapid increase in such pressure, as compared to the pressure of the drilling fluid entering the well bore, utilize to indicate a severing of the core, and such indication employed to manually or automatically actuate a means for receiving the severed portion of the core at the top of the borehole.

The wearing away of the cutting element of the trepan is indicated by a rather sudden reduction in the rate of advance of the stem, and in the pressure of the drilling fluid inside the stem with relation to that outside; the stem may then be pulled and the used trepan replaced by a new one, and boring continued as described above.

As the depth of the borehole increases, a point will be reached where it is no longer economical to pull and replace the trepan. Then the whole stem and trepan is left in the borehole, cemented in place and the stem cut at the top of the casing and firmly sealed to it, and a new trepan and stem of lesser diameter than the first (related to the first as that was to the casing) is introduced. Boring can then proceed as described above for the first stem. This process of nesting drill stems can proceed until the borehole reaches the required depth.

In some cases, such as very deep boreholes where the inertia of the drill string is great, it may be economical or otherwise desirable to rotate the trepan by means of a downhole driving means (not forming part of this invention) driven by the drilling fluid in circulation, inserted between the trepan body and the drill stem. This would avoid the loss of power due to the inertia and friction occasioned by the starting and rotating of the whole drill string at boring speed, though the string should be slowly rotated to reduce the probability of binding in the borehole, while rotation is being resisted to resist the boring torque of the downhole driving means.

While the drilling fluid may be any suitable fluid, divers possible fluids have been considered. Liquid petroleum gas (LPG) seems the most promising, owing to its ready availability at present and its tendency to vaporize at relatively low pressures and to expand, which will help lift the core to the recovery point. Even crude petroleum is suitable, as well as mixtures of petroleum products. At depths where the temperature is above the melting point of sulphur, molten sulphur would serve. For great depths where pressures and temperatures are very high it may be necessary to use a fluid prepared from one or more of the metallic elements, such as mercury and the materials now being used in atomic power plants for conveying energy from reactor to turbine.

In following my method, as will readily be understood by those versed in the art, blow-outs are practically imi. The method of geoboring geological formations to form a borehole comprising the following steps: setting and cementing a suitable conductor pipe or casing; attaching a suitable wellhead to the upper end of said casing whereby a suitable drilling fluid may be circulated under controlled pressures; inserting through the wellhead into the casing a suitable trepan having a cylindrical body with cutting teeth at one end extending inwardly and outwardly so as to cut an annular groove of diameters such as to leave an annular space between the outer surface of the trepan body and the wall of the borehole sulficient to admit to the trepan cutting edges the desired quantity of drilling fluid, and such as to leave an annular space between the inner surface of the trepan body and the cylindrical surface of the core left within the annular groove cut by the trepan no more than suflicient for the return of the drilling fluid and cuttings; connecting to the butt end of the trepan body a hollow drill pipe or stem having uniform inside and outside diameters substantially equal to those of the trepan body; advancing the trepan to the bottom of the bore hole and adding sections of drill pipe as necessary; introducing a suitable drilling fluid through the well head to fill it and the borehole inside and outside the drill stern; maintaining the pressure of the drilling fluid outside the drill stem slightly higher than the formation pressure in the borehole; reducing the pressure inside the drill stem in order to circulate the drilling fluid from outside the trepan to inside the trepan and returning to the wellhead; retracting the drill stem slightly from the bottom of the borehole to free the trepan; commencing the rotating of the trepan and maintaining such rotation until it reaches the desired operating speed and then advancing the trepan to the bottom of the borehole while simultaneously adjusting the pressures of the drilling fluid inside and outside the trepan to maintain a desired rate of flow of the drilling fluid; cutting in the formation an annular groove of diameters determined by the diameters of the outside and inside edges of the trepan teeth; continuously adjusting the pressure of the trepan on the bottom of the borehole to maintain an optimum rate of advance of the geoboring without exceeding a safe torque on the drill stern; transporting the cuttings from the annular groove and naturally freed pieces of core with the returning drilling fluid to the wellhead; separating the cuttings and pieces of core from the returned drilling fluid; severing the upper portion of a standing core cut by the trepan from the portion of the core therebelow; driving the severed portion of the core through the drill stem to the wellhead by piston action; and removing the severed portion of the core.

2. The method of geoboring as set forth in claim 1 and restarting boring of the borehole after any stoppage by the following procedure: reducing the pressure inside the drill stem in order to circulate the drilling fluid from outside to inside the trepan and return to the well head, retracting the drill stem slightly from the bottom of the borehole to free the trepan, starting rotating the trepan and maintaining such rotation until it reaches the desired operating speed and then advancing the trepan to the bottom of the borehole while simultaneously adjusting the pressures of the drilling fluid inside and outside the trepan to maintain the desired rate of flow of the drilling fluid, and Continuing boring as set forth in claim 1.

3. The method of geoboring as set forth in claim 1 wherein the standing core is severed by manipulating the pressures of the drilling fluid inside the drill string until the friction upon the core of the drilling fluid and cuttings returning through the annular space between the core and the drill stem creates suflicient pull on the core to cause severance of the core through tension.

4. The method of geoboring as set forth in claim it wherein the standing core is severed by increasing the pressure of the drilling fluid until the core is severed by virtue of the lateral pressure of the drilling fluid on the standing core.

5. The method of geoboring as set forth in claim 1 and by a suitable means detecting a rapid drop in the differential pressure of the drilling fluid exiting from the borehole as compared to the pressure of the drilling fluid entering the borehole indicating a severance of a core, and actuating a means for receiving the severed portion of the core at the wellhead.

6. The method of geoboring as set forth in claim 1 and continuously measuring, recording and controlling the torque on the trepan and the drill stem to maintain the optimum boring conditions by controlling the speed of rotation of the trepan and the pressure of the trepan on the formation being bored.

7. The method of geoboring as set forth in claim 1 wherein the trepan is rotated by a down-hole means located between the drill stem and the trepan body.

8. The method of geoboring as set forth in claim 1 and utilizing petroleum products as a drilling fluid.

9. The method of geoboring as set forth in claim 1 and utilizing as drilling fluid, a fluid selected from the group consisting of petroleum products and molten sulphur.

10. The method of geoboring as set forth in claim 1 and utilizing as a drilling fluid a fluid including any of the metallic elements.

11. The method of geoboring as set forth in claim 1 and continuing the boring until the trepan becomes unserviceable; cementing the drill string in the borehole; severing the drill stem at the end of the casing; sealing the severed end of the drill stem to the end of the casing; inserting through the wellhead into the first drill stem a second drill string related in diameter to the first drill stem as the first drill string was related in diameter to the casing, and which includes a second trepan and a second drill stem; and continuing the geoboring of the borehole.

12. The method of geoboring as set forth in claim 1 and continuing the boring until the trepan becomes unserviceable;'cementing the drill string in the borehole; severing the drill stem at the end of the casing; sealing the severed end of the drill stem to the end of the casing; inserting through the wellhead into the first drill stem a second drill string related in diameter to the first drill stem as the first drill string was related in diameter to the casing, and which includes a second trepan and a second drill stem; continuing the geoboring of the borehole; and continuing the introduction into the borehole of successive drill strings with stems and trepans of successively smaller diameter as required, by cementing the immediately preceding drill string in place and severing said immediately preceding drill stem at the Well head and sealing the severed end of the immediately preceding drill stem to the severed end of the drill stem immediately therebefore.

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Us. 01. X.R. 

